A Look at “Flow and Pull Value”

Ken Snyder

“Flow and Pull Value” is a principle in the Continuous Improvement dimension of the Shingo Model. This principle seems to be the most difficult for students of the Model to understand. The confusion experienced in learning this principle has caused us deep reflection on how we might better explain and teach this principle.

Causes

In looking at the causes of the confusion, we realized some problems in the way we describe this principle, which, in turn, affects how we teach this principle. Specifically, we noted four problem areas:

  • Two Different Principles. The biggest problem we identified is that we mashed together two separate principles. In other words, there is a principle about “flow” and a separate principle about “pull.” The two are related, but in much the same way many principles are related to other principles. Because we combined these principles, people understood them to be the same principle, which led to the confusion. The fact is, we have seen organizations that have good “flow” but do not have “pull.” Actually, Toyota is an example of this. Toyota builds to dealer inventory and not in response to a specific customer order. We have also seen organizations that have “pull” but do not have flow. This condition is common in the construction industry – buildings usually are not started until there is a contract in place with the customer, but may take several years to build.
  • Verb or Noun? To help students of the Model understand the principles better, we tried to combine the core principle subject with an action verb. Examples include respect (action verb) every individual (subject), focus on (action verb) process (subject), etc. The original intention of the wording of this principle was for “flow and pull” to be action verbs and “value” to be the subject. However, “flow” and “pull” refer to a state of being – which makes them the subject. One can’t “flow” anything. One might be able to “pull” something, but in the context of operational excellence, “pull” doesn’t mean someone “pulls” something, but rather it means someone reacts to “pull” from the customer. This confusion between the action verb and subject adds to the confusion in the current wording of this principle.
  • “Value?” With both “flow” and “pull” as additional subjects, the initial subject, “value,” is confused. This confusion is compounded by the “value” in the principle “Create Value for the Customer.” Is the “value” referred to in this principle the same as the “value” in the “Create Value for the Customer” principle? If it is, then it is redundant (un-Lean!). If it isn’t, then it is even more confusing.
  • Not Natural. A contributing factor to the confusion is that “flow” is not something that comes naturally to humans. Give humans a repetitive task, and they immediately begin to do the task in batches. We’ve tested this with children and with untrained operators many times.

It is easy to see how students of the Model might get confused when studying these principles.

Improvement

To improve this confusing situation, we will do the following:

  • Split the current wording of “Flow and Pull Value” into two different principles – one with the subject of “flow” and the other with the subject of “pull.”
  • Add action verbs appropriate to the definitions of the principle to help explain the meaning.
  • Discontinue the use of the word “value” from either wording with the understanding that both “flow” and “pull” need to “create value” as per the principle of “Create Value for the Customer.”

We propose the following wording of these two principles:

  • “Increase Flow”
  • “Respond to Pull”

“Increase Flow”

“Flow” refers to the movement of the product or service through the value stream. “Flow” is increased by identifying and removing anything from the process that does not add value. “Flow” can be measured by the total elapsed time from start-to-finish, including value-adding work and necessary non-value-added items, including the following delays:

Process Delay. Commonly referred to as “Queue Time,” process delay occurs when a lot arrives at the next process before the process needs it. Process delay has many causes including scheduling issues, part shortages, equipment breakdowns, or quality problems.[1]

Lot Delay. This occurs when all items in a lot must wait for the entire lot to be completed before they are transferred to the next process. The ideal lot size is one – i.e., one product at a time, one operation at a time, one procedure at a time, one transaction at a time, etc., as this reduces lot delay to one piece. To effectively reduce lot delay, set-up times and transportation time must be reduced.[2]

Transport. Time taken to convey material (including patients in the case of healthcare) between operations is often significant. Transport time can be reduced to seconds if all operations are placed right next to each other, creating a flow configuration referred to as a cell. When one-piece flow is achieved, both process and lot delays are reduced to the minimum level, and the cell is said to have continuous flow – that is the ability to process one-by-one, thereby leveling production by product, and creating a high level of just-in-time production.

Inspection. Inability to assure quality at the source adds many inspection points in a process. Cellular arrangement facilitates inspection at the source, and tightly links all operations in the process providing immediate feedback to upstream operations, thereby reducing additional inspection time.

“Respond to Pull”

Shigeo Shingo referred to products and services produced as needed by the customer as “authorized” because production was triggered by an actual purchase order, or “pull,” by the customer. In this way, only needed items are produced as opposed to items produced to a forecast ahead of actual customer need. Producing to forecast was described by Dr. Shingo as “speculative,” and is also referred to as “push,” because items are produced by an upstream process and then “pushed” downstream whether they are needed or not. “Push” often results in inventory and overproduction waste. Pull production conserves valuable resources, shortens customer lead-time, and increases value to the customer. “Pull” can only be achieved when the lead time (i.e., the “flow” of the product or service) is less than the customers’ expected delivery time. Responding to pull is the only way to ensure that the right product or service is provided at the right time, and in the right amount.

Interestingly, performing work without a pull from the market is primarily a manufacturing issue. In healthcare, one would not consider performing surgery on a patient in anticipation of future demand. In financial services, one would not consider processing a transaction for a client in anticipation of future demand. Many organizations naturally adhere to this principle.

Summary

  • “Increase Flow”
  • “Respond to Pull”

[1] Adapted from Shingo, Shigeo, Non-Stock Production: The Shingo System for Continuous Improvement, Productivity Press, 1988, p. 8-9

[2] Adapted from Shingo, Shigeo, Non-Stock Production: The Shingo System for Continuous Improvement, Productivity Press, 1988, p. 9

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